US2240931A - View finder for aerial cameras - Google Patents

Description

May 6, 1941. M, M. HURD ZM.

VIEW FINDER FOR AERIAL CAMERAS Filed Jan. 25, 1939 Patented May 6, 1941 UNITED STATES PATENT OFFICE VIEW FINDER. FOB. AERIAL CAMERAS Mark M. Hurd, Minneapolis, Minn., assigner to Mark Hurd Manufacturing Corporation, Minneapolil, Minn., a corporation o! Minnesota Application January 23, 1939, Serial No. 252,385

My invention relates to photographic apparatus and particularly to view-linders for aerial cameras.

In aerial photography such as for map-making purposes it is not only necessary that the camera always be leveled so that the lens axis is vertically disposed if accurate maps are to be obtained, but it is also highly desirable, from the standpoint of efilciency and convenience, that the camera. be so adjusted rotatively about the lens axis thereof that the lines representing'. the boundaries of a rectangular area of illm in position to be exposed be disposed parallel to which the separate view-finder has been set may change before the camera-positioning operation has been completed and an exposure has been 1 made.

sighting means for a camera enabling pointing the natural co-ordinates of the land areas to be photographed, as, for example, roads extending ln respective directions at right angles to each other. It the airplane in which the aerial camera is lbeing carried is following a track parallel to one of the roads mentioned above and a cross wind condition exists, the longitudinal axis o! the airplane will be disposed at an angle to the track being followed and this angle will vary in proportion to the relation of the wind velocity to the air speed of the airplane. Also, during a run, the direction or the velocity of the wind is likely to vary and the angle mentioned will vary in accordance. The angle between a selected boundary of the film and the longitudinal axis of the airplane must at all times be maintained such that the selected nlm boundary line will be parallel to the track of the airplane regardless of how the angle between the longitudinal axis and the track of the airplane may vary. It should be apparent that the camera must be frequently re-adjusted in position relative to the airplane not only because of changing wind conditions, but also because an airplane cannot be so accurately operated as to maintain a xed direction oi its longitudinal axis throughout a substantial period of time. At the present time, with some kinds of aerial cameras, it is customary to adjust and re-adjust the position of the camera in accordance with observations taken by means of aview-tlnding device separate from and independent of the camera. This type of view-ilnding device is ilrst adjusted in position and a reading is taken from a scale included therein. 'Ihe camera is then rotatively adjusted to obtain a setting thereof corresponding to the reading and is leveled in accordance with observations oi' spirit levels mounted on the camera or the camera mounting. Such methods of properly positioning a camera are inconvenient and consume considerable time. Also the conditions for of the camera in much the same manner as a gun is pointed iby use of the sights thereof.

Another object is to provide one or more viewilnding lenses on the adjustable mounting lor a camera with the axes of such lenses disposed parallel to the lens axis o! the camera carried by the mounting.

Still another object is to provide such a device wherein the lenses are of a type known as negative lenses so that the angie of view aordeo. thereby is similar to the angle of View of the camera when the eyes ot the user are at a suitable distance irom the device.

Yet another object is to provide such a device including a pair of sighting elements associated with the view-i'lnding lens and both situated on the optical axis thereof in spaced relation with each other so that a user of the device may sight past said elements to locate the point on the ground which is at the center of the ileld oi view of the camera.

A further object is to provide such a device of simple, light. compact and inexpensive construction.

These and other objects and advantages oi the invention will more fully appear from the following description made in connection with the accompanying drawing, wherein like reference characters refer to the same parts throughout the views, and in which:

Fig. l is a top view of a portion of the door o! an airplane fuselage carrying a camera mounting and camera with which an embodiment of my invention is associated;

Fig. 2 is a side view oi' the structure illustrated in Fig. l:

Fig. 3 is a top view of the camera mounting of Fig. 1;

Fig. 4. is a sectional view taken along the line l--4 of Fig. 3 as indicated by the arrows;

Fig. 5 is a perspective view of sighting means associated with the view-ilnding lenses of my device:

Fig. 6 is a longitudinal sectional view of one of the lenses of my device with the sighting means of Fig. associated therewith, and

Fig. 7 is a cross sectional view of the lens and associated sighting means of Fig. 6.

Referring to the drawing, the numerals I and 9 refer to the floor and the belly covering oi? an airplane respectively. The floor l and covering 9 are provided with respective vertically aligned apertures la and 9a to function as a downwardly facing window above which a ccmera may be mounted and through which land below the airplane may be viewed by the camera.`

A camera mounting M carrying a camera C is secured to the floor 8 in such position that the lens cone III of the camera C projects downwardly through the aperture Ba in generally centered relation therewith. The mounting M includes a sleeve II of large diameter relative to its length and having an outwardly projecting flange IIa formed at the lower edge thereof and provided with apertures at respective circumferentially spaced points. A pair of elastic, compressible, axially apertured cylindrical shock-absorbing elements I2 are placed respectively above and below each of the apertured portions of the flange I Ia. A dat annular member I! encircling the aperture la is secured to the upper side of the floor I by any suitable means. The member Il is apertured to receive a series of bolts I4 which extend through aligned apertures of the member Il, the elements I! and the flange IIa to secure the sleeve II to the annular member Il.

An annular race member or outer ring I5 having an inner peripheral surface of an upwardly divergent partial spherical shape is mounted on the upper end of the sleeve I I. The lower edge of the race member I5 is provided with a downwardly projecting annular projection Ia which is telescoped into the upper end of the sleeve II and is secured therein by suitable means such as the screws which project inwardly through suitably located apertures in the upper marginal portion oi' the sleeve Il and are screw-threadedly received in suitably located internally screw-threaded apertured portions of the projection lia.

A centrally apertured circular body or inner ring I1, of which the lower portion of the exterior peripheral surface is shaped complementary to the interior peripheral shape of the race member I5, is set in the race member Il so as to be supported thereby and yet be rotatable and tiltable relative thereto. The body I1 is provided, in the portion of the periphery thereof working in the race member Il, with a multiplicity of ball bearings Il rotatably carried in suitable recesses in the periphery of the body I1 for rolling engagement with the race member I8.

The camera C is fixedly mounted on the body I1 by any suitable means so as to be rotatable about its lens axis and tiltable relative to the race member Il with the body I1. The lens cone of the camera C projects downwardly through the central aperture of the body I1.

All of the above described structure is of conventional design and a description of an embodiment of my invention associated therewith follows.

In four respective quadrants thereof the body I1 is apertured to receive my view-finding lenses which are preferably but not necessarily of generally rectangular shape. One of my lenses I! is secured in each o the above mentioned apertured portions of the body I1 with the optical axes of the lenses I8 positioned to be disposed parallel to the optical axis of the lens of a camera C carried by the body I1 in the normal position relative thereto. A view through each of my lenses Il of the ground below is afforded through the aperture of the body I1 accommodating the lens, the interior of the sleeve II and the aper tures la and 9a. While my lenses are of generally rectangular shape the sides thereof toward the periphery of the body are curved somewhat. as shown, to conform approximately with the curvature of a circle extending along said sides and having a center common with the center of the body I1.

My lenses I9 are of the type known as a negative lens and which is exemplified by the planoconcave lens shape illustrated in Figs. '1 and 6. This type of lens is employed so that the area which may be viewed through the lens I! will be substantially the area viewed by the camera C when the eyes of the user are situated at a suitable distance above the lens I9.

Each 4of my lenses I! is provided with sighting means whereby a sight may be taken along the optical axis of the lens to locate the point on the ground below constituting the center of the area viewed by the camera C. One form which my sighting means may take is illustrated in detail to an enlarged scale in Figs. 5, 6 and '1. Before the lenses I0 are placed in the apertures provided for them in the body I1 clips 20 are placed on each of the four sides of the lens. The clips 20 may consist of strips of metal bent at rightangles at each end so that the bent end portions of each clip may engage respectively the top and bottom sides of the lens Il while the medial portion of the clip 20 extends across the edge or side surface of the lens I0 from the top to the bottom of the lens I9. With the clips 20 in place on the lens I9, the lens may be placed in the aperture provided therefor in the body I1. Above the lens I0 a wire 2| is soldered or otherwise secured to the upper ends oi the clips 2l disposed at respective ends of the lens Il. Another wire 22 is secured at its respective ends to the upper ends of clips 20 situated at longitudinal edges of the lens Il. The wires ZI and 22 are pulled upwardly at their centers to intersect in the manner of cross hairs at a point above the lens I8 and on the axis of the lens I9. In a similar manner wires 2l and 2l are secured to the bottom ends of the clips III and are pulled downwardly to intersect at their centers at a point below the lens I9 and on the axis of the lens Il. It should be apparent that a user oi the device may sight again the optical axis of the lens Il by so positioning the wire that the intersections of the wires respectively above and below the lens I8 coincide as seen by the user. With the user's eye in such position a point on the ground below which is aligned with the two intersections of the sighting cross wires will represent the center of the area viewed by the camera C. In cases where the utmost accuracy is not necessary either the upper or lower pair of crossed wires may be omitted and crossed lines formed on the corresponding face of the lens Il, as by etching, may be substituted therefor as indicated in connection with the right-hand lens of Fig. 4. If still less accuracy is required. the two pairs of cross wires could be replaced by pairs of crossed lines placed respectively on the upper and lower sides oi the lens II. In all cases where a pair of crossed lines is placed on the course, be situated at the optical axis of the lens I8, and the lines would be disposed parallel to respective edges of a. rectangular area of film positioned in the camera C for exposure.

In use of my combination of a camera, camera mounting, viewing lenses and sighting elements the operator of the camera may sight through any one of the lenses i8 and, where one or more pairs of cross wires are used', may adjust the position of the camera so that the crossed wires are parallel to natural coordinates of the area being photographed such as, for example, intersecting roads or the like. The sighting points formed by the intersections of the two pairs of wires are aligned with a point on the ground directly below the camera at all times when the camera is properly leveled. Obviously. in operating the camera to make an exposure, the operator may readiust the position of the camera as the airplane may swing this way or that so as to maintain the camera in proper position both preceding and during the process of making an exposure. The camera may be aimed in much the same manner as a gun. It should be apparent that the camera may be properly positioned quite rapidly and conveniently and may be easily maintained in proper position during the process of making an exposure. The customary procedure of using a separate view finder and sighting the camera in accordance with a reading taken on the dial of the separate view finding apparatus is eliminated entirely and the camera pointing operation is direct and rapid. Spirit levels on the camera or its mounting are ordinarily used in conjunction with my view nding device i'oi` the purpose of leveling the camera.

My view finding device is particularly useful in checking the track of a camera-equipped airplane and in taking observations for determining the proper time interval at which to take suitably overlapping pictures.

The availability of four view-finding lenses in mydevice enables observations tobe made of areas not only directly below but also ahead, behind or to either side of the camera-equipped airplane by using such one of the four lenses that the camera cone will not obstruct view through the lens of the area to be observed.

It is apparent that I have invented an improved type of view-finding and aiming apparatus for aerial cameras which enables particularly rapid and'accurate sighting of the camera, and also enables constant readiustment of the camera position t'o compensate for changes in conditions occurring during the process of taking a picture.

It will, of course, be understood that various changes may be made in the form, details, proportions and arrangement of the parts without departing from the scope of my invention.

What is claimed is l. View finding apparatus for a camera mounted on a member which is tiltable and also rotatable about the lens axis of said camera comprising, a lens supported from said member with its optical axis parallel to the lens axis of said camera and being so situated that vision therethrough to the scene viewed by the camera is unobstructed, a pair of relatively thin elongated elements associated with one face of said lens and supported at their ends from said member, said elements being so positioned and so arched away from said lens as to intersect at a point on the optical axis of said lens spaced from said lens, and structure providing a sighting point on said optical axis spaced from the intersection of said wires.

2. View finding apparatus for a camera mounted on a member which is tiltable and also rotatable about the lens axis of said camera comprising, a lens supported from said member with its optical axis parallel to the lens axis of said camera and being so situated that vision therethrough tothe scene viewed by the camera is unobstructed, two lpairs of relatively thin elongated elements associated with respective faces of said lens and supported from their ends from said member, said elements being so positioned and so arched away from said lens that the respective elements of each of said pairs intersect at a point on said optical axis spaced outwardly of the corresponding face `of said lens whereby the two intersections so formed constitute widely spaced sighting points on said optical axis.

3. A combined flexible mounting and view finder for an aerial camera comprising, a ring-shaped base adapted to be secured to the floor of an airplane in registration with an aperture through said floor, a member carried by .said base in registration with the central space thereof and with freedom for limited rotational and tilting adjustive movements relative thereto, said member being arranged for rigid mounting of a downwardly directed camera. thereon in a predetermined position relative thereto and being apertured for visual communication between a camera mounted thereon and a scene therebelow, and a viewfinder lens fixedly mounted on said member in such relation thereto that the axis of said lens will be parallel to the lens axis of a camera mounted on said member, said member having an aperture therethrough registering with said lens.

4. A combined flexible mounting and view finder for an aerial camera comprising, a ring-shaped base adapted to be secured to the floor of an airplane in registration with an aperture in said iioor, a member carried by said base in registration with the central space thereof and with freedom for limited rotational and tilting adjustive movements relative thereto, said member being arranged for rigid mounting of a downwardly directed camera thereon in a predetermined position relative thereto and .being centrally apertured for visual communication between a, camera mounted thereon and a scene therebelow, and a plurality of viewfinder lenses flxedly mounted on said mem-ber at respective sides of the position of a camera mounted thereon, said lenses being positioned with their axes parallel to the position of the lens axis of a camera mounted on said member, said member having apertures therein registering with said respective lenses.

5. A combined flexible mounting and view finder' for an aerial camera comprising, a ring-shaped -base adapted to be secured to the floor of an airplane in registration with an aperture through said floor, a. ring-shaped camera-carrying member supported by and partially within said base with freedom for limited rotational and tilting adjustive movements relative thereto, said member being arranged for rigid mounting of a downwardly directed camera therein with the lens axis of the camera parallel to the axis of said member, land a viewfinder lens mounted on said member with its axis parallel to the axis thereof, said member having an aperture therethrough registering with said viewfinder lens.

6. View nndlns :ppn-stm for en eerlel camera. which ls nmmelly pointed downwerdly comprisinl. en ennuler mounting member tlltsbly mounted and also rotatable about l. tenenl vertical sx1. seid mounting member hsvlns' means for slsomountlnlseldesmerewltntheleneotnld comers, disposed substantially axially o! seid member and below the seme, the periphery of nld emmers being oonsldernbly len than the externsl periphery o! seid member, sud member belnl epex'tured outside of lts eonnectlonwlth snld almere. and o lens mounted ln sold epertured portion with its nils pltlllel to the lens xls of uid camere end so situated on said memberthetvlslontherethmulhtotheeoenevlewed by sold camera. ls unobetmeted.

HARKILHURD.

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